Retreaded tires provide an economical way to gain additional use from tire casings after the original tread or retread has become worn. According to a method of retreading, sometimes referred to as cold process retreading, a worn tire tread and other materials on a used tire are removed to create a buffed, generally textured, treadless surface along the circumference of the tire casing to which a new tread may be bonded.
The tire casing may be inspected for injuries, some of which may be skived and filled with a repair gum while others may be severe enough to warrant rejection of the tire casing. After completion of the skiving process, the buffed surface may be sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Next, a layer of cushion gum may be applied to the back, i.e., the inside surface of a new tread, or alternatively, the layer of cushion gum may be applied directly to the tacky surface on the tire casing. There are other methods that may eliminate the need for cement or cushion gum. The cushion gum is a layer of uncured rubber material. The cushion gum and tread may be applied in combination about the circumference of the tire casing to create a retreaded tire assembly for curing. As an alternative, a length of tire tread may be wrapped around the tire casing with the cushion gum already applied. The cushion gum may form the bond between the tread and the tire casing during curing.
Certain retreading processes such as the buffing of the tire casing are carried out on specialized equipment that rotatably mount the casing onto an expandable rim. The expandable rim may include various sections that move radially outwardly with respect to a central hub, for example to expand to a circumference of the rim and sealably engage the beads of the casing, which may be inflated to provide a resilient surface that can be buffed or otherwise processed. The machine may include a rasp that can be applied to the surface of the tire to remove rubber. Because the circumference of a tire casing can more easily be measured by the operator, the desired final radius of the tire casing may be identified in relation to the final circumference of the tire casing.
Expandable rims may experience wear along the interface of the expanding sections and the central hub. That interface, which may include a sliding contact of radially ramped surfaces, may be subject to considerable wear, especially under operating loads where the rim is expanding against the bead of a casing.